Abergorci (mouth of the Gorci stream) was a farm name in the valley of the Rhondda Fawr, first documented as an anglicised Abergorky in the pedigree of Morgan David Cadwgans in a batch of NLW docs. dated 1611-21. It was written in Welsh orthography as Abergorci in the Land Tax Assessment docs. of 1789 and 1808.

Abergorchwy (1833) is a literary attempt at rationalising the place-name. There seems to be no justification for the Treorchy spelling of 1870, yet it has over the years, remained the favoured anglicised form.

Three coal pits were sunk here in the 1860s, namely Abergorky, CwmPark (park vale) and Tyle Coch (red hill). As Abergorci , the old farm name, was the name of only one of the three newly sunk pits, it would have been inappropriate as the name for the settlement that developed around them. Therefore, the new town was given the name of Treorci (in various guises - Treorkie, Treorchy, Treorki, Treorchwy and Treorky) i.e. ‘town (on the stream called) Gorci'.

Gorci does not mutate after aber (Abergorci) because here, aber is a masculine noun, but it does mutate after tre (Treorci) because tre is a feminine noun.

The etymology of Gorci is difficult and must be allowed to remain a mystery until earlier and more helpful forms are uncovered.

Today Trealaw is the name of a village in the valley of the Rhondda Fawr. Originally Trealaw was the name of a colliery built mainly on the lands of Brithweunydd Uchaf and Isaf farms c1870. The colliery name became the village name.

Trealaw's literal meaning is Alaw’s town, so named after Alaw Goch, the bardic name of landowner/industrialist David Williams (1809-63) of Ynyscynon House, Cwmbach, Aberdare.

David’s son Gwilym (1839-1906) [later to become the renowned Judge Gwilym Williams] named the colliery in honour of his late and much respected father. The village that developed around the colliery adopted the colliery name. All Saints church was erected in Trealaw in 1897.

Brithweunydd Colliery, Trealaw listed in Slaters Directory of 1880 actually closed in 1879. This is not to be confused with Trealaw Colliery.

Pendyrys is known far and wide as the name of a famous male voice choir from the Rhondda Valleys. But many may be surprised to know that there is no village of that name in either the Rhondda Fawr or the Rhondda Fach valleys.

The choir is based at Tylorstown (named after coal owner Alfred Tylor of Newgate, London.) and takes its name from Pendyrys Colliery and the names of two farmsteads – Pendyrys Isaf and Pendyrys Uchaf.

The village was named after coal owner Alfred Tylor, but the choir was named after the place of work of most of its early members.

Pendyrys has two elements – ‘pen’ and the adjective ‘dyrys’ meaning ‘hill of tangled undergrowth’. Paradoxically however, Pendyrys male choir always produced harmonious musical tones of high quality, especially while under the baton of maestro Glyn Jones.